1. Field of the Invention
The present invention relates to an exposure system and method, and particularly to an exposure system and method with group compensation for an exposure device in semiconductor manufacturing.
2. Description of the Related Art
Photolithography is one of the most important technologies in semiconductor manufacturing. It seriously affects structures of MOS devices, such as patterns of layers and doped regions. Typically, the number of masks used in photolithography indicates the complexity of a manufacturing process. As described above, since photolithography is complicated, the exposure device performing the photolithography can create a bottleneck in semiconductor manufacturing.
Exposure of wafers is generally implemented in a “Step and Repeat” fashion to transfer high resolution patterns to the wafers, the exposure device is thus referred to as Stepper. That is to say, the pattern on the mask is projected and sized to one portion or block of the wafer. This is repeatedly implemented for all blocks on the wafer one by one until the entire wafer is exposed.
FIG. 1 illustrates the overlay relation between front-end and back-end processes. In this case, the patterns of layers to be exposed in the respective back-end processes (back-end process 1 (101), back-end process 2 (102) and back-end process 3 (103)) have to overlay those in the front-end process 100. Since only the pattern of one of layers is transferred to the wafer after each block of the wafer is exposed, and there are many patterns of layers and corresponding masks involved in one manufacturing process, addition to piece alignment between the blocks of the wafer and overlay alignment between the patterns of the layers is essential to the photolithography processing step.
However, performance of an exposure device always slightly varies with time. For a precisely accurate exposure, the wafers processed must be measured to compensate for parameters (recipe) used by the exposure device. The recipe will be compensated and used by the exposure device to process the subsequent wafers. In general, the recipe compensation is implemented manually or using a feedback system. Taiwanese Patent 516099 discloses a method and apparatus of wafer exposure with correction feedback that employs a feedback system using a computer system to calculate values and use the values to compensate overlay parameters.
The device and mask used for exposure in the front-end process will affect the compensation for overlay parameters in the back-end processes. However, the conventional system calculates the compensation using mixed calculation, that is the device and mask used for exposure in the front-end process are not considered. Therefore, the compensation calculation for products processed by different devices and masks in the back-end processes will, affect each other, thereby making the compensation calculation unstable, raising the rework rate, and damaging the throughput of the manufacturing process.